High Temperature Gigacycle Fatigue

FEDERICO J. CAVALIERI; DANIELE WAGNER; CLAUDE BATHIAS

Berlín

Congreso; V International conference of VHCF Berlin 2011; 2011

Many components in engines are submitted to vibration that is to say the gigacycle regime. In this paper, the study of an austenitic stainless steel has been chosen in order to illustrate such problem for aircraft turbine disc or thermal engines. Initiation in VHCF due to flaws is a real danger. In order to determine the form of the SN curve between 1E6 and 1E9 cycles, at high temperature, it is necessary to apply an accelerated fatigue testing method based on the ultrasonic technique operating at 20kHz. The most important conclusions obtained are summarized below: - The design of specimens for high temperature tests using FEM modal analysis, showed good agreement with the experimental tests. When the specimen reached the desired temperature, i.e., room temperature, up to 700ºC, resonance frequency was close to 20 kHz during the ultrasonic fatigue test. - The dynamic mechanical properties of alloys subjected to high temperatures were identified based on numerical simulations and the measured resonance frequency of the specimens. - At room temperature, the steel presented an endurance limit. More than 20 specimens were tested and none failed above cycles. - The 600 ºC S-N curve of steel has shown a continuous decreasing stress-life response.. In the specimens tested, the crack initiation was observed on the surface. SEM inspections showed that just one specimen failed by fish-eye rupture mode, from a massive internal inclusion. - The 700 ºC curve showed continuous decreasing stress life-response. The crack initiation was identified on the surface in the failed specimens. - The rupture surface in the room temperature test was normal to the longitudinal axis of the specimen. However, at high temperatures the surface fracture presented an inclination of 40º to the principal stress